1. Field of the Invention
This invention relates to sound board emulation using a digital signal processor.
2. Description of Related Art
There has been a great deal of market demand for audio and video output from computer systems, particularly in the case of personal computer systems known as "PC"s. This has led to the availability of hardware devices for producing audio output in response to commands from a central processing unit (CPU). Such a device may be commonly integrated into a computer system by implementing it on an add-in board, and by coupling the add-in board to a system bus, such as the industry-standard architecture (ISA) or extended ISA (EISA) bus. When coupled to the system bus, the board may be commanded by the CPU, under control of software for producing and playing audio output.
One product for producing audio output is the "Sound Blaster" product, available from Creative Technology, Inc., of Milpitas, Calif. This product, and the interface by which the CPU may command it, has become popular with some segments of the personal computer industry, and its command interface is also commonly used by other devices.
It is desirable for makers of audio-output boards to have the same command interface. Makers of hardware and software for personal computer systems may rely, and will certainly prefer, that any audio-output board have the same command interface. Designer may also wish to avoid multiple versions of a product (designed for compatibility with more than one product's command interface), and may therefore provide a product which uses only one command interface.
One aspect of this common command interface is that it specifies certain named registers that the CPU may access on the audio-output board, either to read values from or to write values into. While this may be an acceptable way for the CPU to command the audio-output board, it is desirable that an audio-output board does not require actual physical registers to implement this aspect of the command interface. For example, an implementation in which these registers are simulated by other physical means may be less expensive, faster, or more easily upgraded.
It is also desirable that an audio-output board does not require an implementation using dedicated hardware for the functions it provides, and may instead be implemented using a digital signal processor (DSP) operating under software control. However, the common command interface described above generally requires that the audio-output board must be immediately responsive to commands from the CPU. This generally requires that the DSP must spend its time watching and waiting for, and responding to, the CPU, and that its additional computing power is therefore wasted.
Accordingly, it is an object of this invention to provide an improved audio-output device.